1. Field of Invention
The present invention relates to a power transmission system of a hybrid electric vehicle. More particularly, the present invention relates to a power transmission system of a hybrid electric vehicle overcoming deterioration of system efficiency due to power reuse, reducing capacity of a motor, raising a weight of mechanical power delivery path in high-speed driving so as to reduce electric load, and enabling of using maximum power of an engine.
2. Description of Related Art
Environmentally-friendly technique of vehicles is very important technique on which survival of future motor industry is dependent. Vehicle makers are focusing on development of environmentally-friendly vehicles so as to meet environment and fuel consumption regulations.
Some examples of the environmentally-friendly vehicles are an electric vehicle (EV) which is a zero emission vehicle (ZEV) and a fuel cell electric vehicle (FCEV). The electric vehicle and the fuel cell electric vehicle have merits of no emission, but have limitation due to technical problems such as capacitance and life of a battery and social infrastructure construction such as charging stations.
Therefore, a hybrid electric vehicle is developed and commercialized. The hybrid electric vehicle generates driving torque by using a conventional internal combustion engine and an electric motor. The hybrid electric vehicle is a vehicle driven by combining electric power and power of an internal combustion engine. Because the internal combustion engine and the electric motor are controlled to operated at high-efficiency operating points according to the hybrid electric vehicle, efficiency may be excellent and exhaust gas may be reduced.
In addition, construction of charging stations that is problems of the electric vehicle is unnecessary, fuel economy can be improved, and travel distances are similar to those of the conventional internal combustion engine vehicle according to the hybrid electric vehicle. Therefore, it is expected that the hybrid electric vehicles feature future environmentally-friendly vehicles.
The hybrid electric vehicle using a power split device such as a planetary gear set is called a power split type hybrid electric vehicle. Power flow of the power split type hybrid electric vehicle includes mechanical flow where engine torque is directly transmitted to an output shaft and electric flow where electricity is generated using the engine torque and a battery is charged by the generated electricity or a motor is driven by energy of the charged battery.
Since the engine can be operated independent from the output shaft in the power split type hybrid electric vehicle, the engine can be freely powered on or off during running and an electric vehicle mode can be achieved. In addition, since a power transmission system of the power split type hybrid electric vehicle can be operated as an electrically variable transmission (EVT) by using two motor/generators, engine may be driven efficiently.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.